1. Field of the Invention
The present invention relates to improvements in a rotary digital audio tape recorder (hereinafter referred to as R-DAT).
2. Description of the Prior Art
In the known R-DAT, generally a rotary cylinder is rotated at a predetermined rate with relative motion of a magnetic tape which is driven while being kept in contact with the peripheral surface of such rotary cylinder through a predetermined lap angle, and a recording or reproducing operation is performed by a pair of recording/reproducing heads on the rotary cylinder with switchover of signals. One conventional example of such R-DAT is schematically shown in FIG. 3, wherein a pair of magnetic heads 2 and 3 are disposed at an angular interval of 180.degree. on a rotary cylinder 1 having a diameter of 30 mm. Each of the magnetic heads 2 and 3 employed in this example serves as a recording/reproducing head. A magnetic tape T is held around the rotary cylinder 1 at a predetermined track angle by means of conical tape guides 4 and 5 while being kept in contact with the peripheral surface of the cylinder 1 through a lap angle of 90.degree. . As the magnetic tape T is moved relatively to the rotary cylinder 1 driven at a rate of 2000 rpm, the magnetic heads 2 and 3 alternately function to perform a recording or reproducing operation on the magnetic tape T. According to the above R-DAT, there are attainable some advantages including a sufficient head output and a high signal reproducibility with a satisfactory signal-to-noise ratio. On the other hand, there also exists a disadvantage that the whole structure becomes dimensionally large since the rotary cylinder has a great diameter of 30 mm.
Meanwhile, on the basis of the principle that the lap angle and the cylinder diameter are in inverse proportion, another exemplary R-DAT may be contrived as shown in FIG. 4, wherein the diameter of a cylinder 1 is reduced to 15 mm which is one half of the diameter in the foregoing example and the lap angle .theta.2 is widened to 180.degree.. In this R-DAT where the cylinder diameter is small, the whole structure can be dimensionally diminished to have a reduced thickness and still the interchangeability of the magnetic tape T is maintained. However, since the rotation rate of the cylinder 1 is kept at a fixed value of 2000 rpm, the relative running speed of the magnetic tape T is lowered due to the smaller cylinder diameter, and therefore it is unavoidable that the head output is decreased with deterioration of the signal-to-noise ratio in reproduction.